1. Field of the Invention
This invention relates to an improved apparatus for hydraulic control of braking or of a clutch in a motor vehicle, in which an emitter or receiver cylinder includes a rear guide tube which is telescoped axially in a main body of the cylinder.
More particularly, the invention relates to apparatus for the hydraulic control of a motor vehicle clutch, of the type comprising at least one control cylinder, wherein the cylinder comprises a substantially tubular cylinder body in which there slides axially a piston which delimits, through a front transverse face, a cylindrical hydraulic chamber, wherein a port for connection of a duct is open into the hydraulic chamber, and wherein the cylinder body is made in at least two parts of synthetic material such as plastics material, which parts comprise a main body and a rear guide tube which is mounted within a rear part of the main body, and which participates in the guiding of the piston in the cylinder.
2. Description of Related Art
A cylinder of this type is known, and was in particular described and shown in European patent application EP-A-0 345 451.
In that document, the rear tube and the main body are made of plastics material, and each of them is provided with a screw thread so as to enable the rear tube to be assembled into the main body in a screwing operation.
This type of assembly has the disadvantage that it is delicate to carry out and relatively fragile, given that the components are made of plastics material.
In addition, screwed assembly makes it necessary to provide between the rear tube and the main body a radial clearance which is large enough to enable the screwing operation to take place and to compensate for any errors in the form of the screw thread.
As a result, it is not possible to guarantee that the rear tube and the main body will be perfectly coaxial with each other, although it is necessary that they are, in order to guarantee good sliding movement of the piston in the cylinder.
With a view to providing a solution to these problems, an arrangement is described in the document FR-A-2 741 920 in which the rear tube and the main body are in cooperation through complementary cylindrical surfaces so as to enable the rear tube to be assembled in the main body by axial telescoping.
The rear tube is secured in the main body by welding or by sealed adhesive bonding.
The adhesive bonding or welding is carried out at least partly between the two complementary cylindrical surfaces of the rear tube and main body.
The rear tube carries at least one annular dynamic sealing member which is interposed between the piston and the rear tube so as to seal the hydraulic chamber.
The cylinder body is made of plastics material and the piston is made of metal.
This arrangement does give satisfaction, but in the case of a weld, it is necessary to protect the dynamic sealing member. In addition it is desirable to have components of plastics material which are of simple design.
An object of the present invention is to respond to these desires.
According to the invention, an apparatus of the type described above is characterised in that the welding of the rear tube to the main body is carried out locally by indirect application of heat with the aid of at least one energy source of the laser type.
Thanks to the invention, the dynamic sealing member is protected because the welding operation is performed locally, and with precision, by indirect application of heat using a laser beam.
In addition, by contrast with a weld of the ultrasonic type, no vibration is transmitted to the rear tube and main body, which also enables these components to be protected, as well as the dynamic sealing member.
The solution according to the invention is therefore less costly because it enables components to be made to simplified designs as compared with components which are welded together ultrasonically.
In this connection, this method of assembly allows increased freedom of design for the components because there is no need to bring a sonotrode as close as possible to the zone to be welded, as is the case with ultrasonic welding. The weld plane can be inclined. It is possible to weld the rear tube with the main body in several zones, and one of the zones can be continuous while the other is not. New forms can be envisaged, especially with a view to standardisation of the control cylinder.
Thus, in a preferred embodiment, the cylinder body is made in three parts, and includes a central part which is arranged between a blind front part and the rear tube which constitutes a guide jacket. The main body is thus in two parts, namely the front part defining the hydraulic chamber and the central part which constitutes the rear portion of the main body in which the rear guide tube is fixed. The sealing member is lodged within the central part, which preferably has fastening means such as ears for fastening to a fixed part of the vehicle.
In order to complete the weld, the telescopic engagement of the rear tube in the main body is carried out with radial gripping, for example by force-fitting.
Preferably, the radiation in the form of a beam emitted by the laser is in the infrared radiation range, so that the main body and the rear guide tube can be made of mouldable plastics material which is inexpensive, for example material based on filled or unfilled polyamide.
When the laser is located externally, the main body is in material transparent to infrared radiation, while the rear tube absorbs infrared radiation. In one embodiment, this tube is of a material different from that of the main body. In another version, the material is identical, but the rear tube contains at least one additive such as pigment, for example 1 to 2% of carbon, for absorbing the infrared radiation.
Thus the infrared beam emitted by the laser passes through the transparent component without degrading it, and superficially heats the absorbent component which contains the additives.
During this welding operation, it is possible, if desired, to turn the component with respect to the laser beam, and vice versa.